The present invention relates to the art of earth boring and, more particularly, to a rolling cone cutter earth boring bit. Earth boring bits of this type are adapted to be connected as a lower member of a rotary drill string. As the drill string is rotated, the bit disintegrates the formations to form an earth borehole. Generally, the bit includes a multiplicity of individual arms that extend angularly downward from the main body of the bit. The lower end of each arm is shaped to form a spindle or bearing pin. A rolling cone cutter is mounted upon each bearing pin and adapted to rotate thereon. Individual bearing systems promote rotation of the rolling cone cutter. These bearing systems have traditionally been roller bearings, ball bearings, friction bearings or a combination of the aforementioned bearings. The rolling cone cutters include cutting structure on their outer surfaces that serves to disintegrate the formations as the bit is rotated.
In addition to rotational forces, the bit is subjected to a thrust load during the earth boring operation. The weight of the drill string and/or the downward force applied by the rotary drilling equipment apply a substantial thrust load upon the earth boring bit. Since the thrust load is applied axially to the bit, a specific load area is produced on the lower side of each bearing pin. As the bit is rotated and moved through the earth formations, the load area tends to wear. This wear can result in erratic movement of the rolling cone cutter upon the bearing pin. Such erratic movement can cause difficulties with the sealing system of the bit. Further, the wear in the load area tends to deteriorate the bearing surface and reduces the lifetime of the bit.
In order to obtain high penetration rates with a rotary rock bit in some formations, it is necessary to apply heavy loads on the bit and to operate the bit at a moderate speed. With other formations only moderate loads are required, but the bit must be operated at relatively high speeds. The rotary rock bit operates under a highly corrosive environment and is subjected to temperature extremes. The drilling operation is often conducted thousands of feet underground wherein elevated temperatures are encountered. The bit is continually flushed by circulating drilling fluid to cool the bit and carry away the drill cuttings. This fluid is generally water with chemicals added to control water loss or to control viscosity and/or pH. These chemicals produce a corrosive drilling fluid. The drill cuttings, the materials encountered in the earth formations, barites added for fluid weight control, and the chemical composition of the drilling fluid combine to create a corrosive and abrasive drilling environment. In view of the previsously explained circumstances, it can be appreciated that a bearing system for a rotary rock bit must be constructed so that it will include exceptional performance characteristics within a limited geometrical configuration. Since the entire drill string must be withdrawn to replace a bit should it fail, it is highly desirable to have the bearing systems of the bit operate for an extended period of time.